Download Myotonic Dystrophy Type I (Steinert`s Disease)

Myotonic Dystrophy Type I (Steinert’s Disease)
What is myotonic dystrophy?
Myotonic dystrophy type I (DM1),
also known as Steinert’s disease,
is the most common form of
adult-onset muscular dystrophy
affecting approximately 1 in
8,000 people worldwide. It is
characterized by progressive
muscle weakness and difficulty
in relaxing the muscles after they
have been contracted (myotonia).
However, it is misleading to think
of myotonic dystrophy as only a
muscle disorder because so many
of the body’s systems may be
affected. DM1 commonly impacts
a person’s heart, breathing, vision,
gastrointestinal and reproductive
systems, as well as cognition.
Who can be affected by myotonic dystrophy?
Myotonic dystrophy can affect people at any age.
The majority of people are diagnosed by the time
they reach their early twenties. With each generation,
symptoms are more severe than the prior generation.
This is known as anticipation.
What are the different forms of myotonic
dystrophy?
Myotonic dystrophy type I (DM1) has two forms:
an adult form and a congenital form. Congenital
myotonic dystrophy, the most severe form of
myotonic dystrophy, is present at birth. It is almost
always passed to the child from an affected mother.
When the father has myotonic dystrophy, his
children are not at risk for developing the congenital
form. Babies with congenital myotonic dystrophy
are very weak and frequently have problems sucking,
feeding, and breathing. If they survive the newborn
stage, they generally overcome their breathing and
feeding problems, but they are slow to develop
language and motor skills and are often affected for
life with difficulties in these areas.
With the adult form of DM1, symptoms
generally appear between the ages of 10 and 40
years. The severity of symptoms, rate of progression,
and degree of disability vary widely from one person
to the next, even among family members. In most
cases, the disorder progresses slowly.
Myotonic dystrophy type II (DM2) - also
known as proximal myotonic myopathy - is a milder
and more rare form of myotonic dystrophy. The
disease development and progression resembles
DM1, however, unlike DM1, DM2 does not exhibit
anticipation (the tendency of the disease to become
more severe with successive generations).
What causes myotonic dystrophy?
In patients with myotonic dystrophy, there is a
problem with a particular gene that causes it to
convey faulty instructions. This mistake results in
National Office:
2345 Yonge Street, Suite 900, Toronto, Ontario M4P 2E5
T 416.488.0030 1.866.MUSCLE.8 F 416.488.7523 W muscle.ca
Myotonic Dystrophy Type I (Steinert’s Disease) / page 2
the symptoms of DM. The two types of myotonic
dystrophy are caused by mutations in different
genes. Although DM1 and DM2 show similar
symptoms, they have fundamentally different
origins.
Type 1. The genes responsible are found on
chromosome 19. Each chromosome consists of
a long chain of chemicals that form the units of
DNA. These units are called nucleotide bases.
The disease is characterized by stretches of DNA
(abbreviated CTG) on the DMPK (dystrophiamyotonic protein kinase) gene that are repeated
several times. It is sometimes referred to as a
trinucleotide repeat disease because of the repetition
of these three DNA base pairs.
In healthy people, there are between 5 and 37
repeats of the CTG sequence. People with myotonic
dystrophy type 1 have expanded repeats which
can contain anywhere from 50 to more than 4,000
repeats of the CTG sequence.
Type 2. The genes responsible are found on
chromosome 3. The repeat sequences contain
stretches of DNA in which four chemicals
(abbreviated CCTG) on the Znf9 (zinc finger
protein 9) gene are repeated. As in DM1, the
disease occurs after the number of repeats exceeds
a certain threshold. Healthy individuals have fewer
than 75 CCTG repeats. People with DM2 can have
anywhere between 75 and 11,000 repeats.
How is myotonic dystrophy inherited?
Myotonic dystrophy is transmitted by an autosomal
dominant pattern of inheritance. “Autosomal” refers
to any of the 22 chromosomes not associated with
determining the sex of the child. “Dominant” means
that one copy of the mutated gene is enough to
cause the disease. There is no carrier status. Each
child born to an affected parent has a 50% chance
of inheriting mutated gene and developing the
disorder, and a 50% chance of being unaffected.
The mutated gene can be passed to male and female
children with equal frequency.
What are the symptoms of myotonic
dystrophy?
Myotonic dystrophy is a very complex condition.
It involves many of the body’s systems, and there
are a wide variability of symptoms. Symptoms may
include:
• Trouble relaxing a muscle (myotonia)
• Muscle weakness (myopathy)
• Muscle stiffness
• Drooping eyelids (ptosis)
• Delayed and/or impaired speech
• Difficulty raising the head when lying
• Difficulty holding or lifting an object
• A shuffling gait
• Difficulty climbing stairs or rising from a seated
position
• Cataracts, which develop fairly slowly but can
occur in people as young as 30 years
• Abnormal heartbeat or dizzy spells
• Difficulty swallowing
• Bowel problems, such as constipation and
stomach pain
• Reproductive challenges
• Respiratory problems, such as infections and
shortness of breath
• Premature balding or thinning of hair
• Excessive daytime sleepiness
How is myotonic dystrophy diagnosed?
Diagnosis is made by a physician based on family
history, a physical examination and tests, such as:
• genetic testing
• electromyography (EMG) to measure electrical
activity in the muscle
• muscle biopsy
National Office:
2345 Yonge Street, Suite 900, Toronto, Ontario M4P 2E5
T 416.488.0030 1.866.MUSCLE.8 F 416.488.7523 W muscle.ca
Myotonic Dystrophy Type I (Steinert’s Disease) / page 3
Is there any cure or treatment for myotonic
dystrophy?
Efforts to find a cure for myotonic dystrophy are
ongoing. At present there is no treatment that will
slow or stop the disease progression. The treatments
that are currently available are symptom oriented.
For example:
• Surgery for correction of cataracts
• Medication may be prescribed to counter the
effects of myotonia
• Medication and/or surgery to address heart
problems or excessive daytime sleepiness
• Speech and physical therapy
• Occupational therapy to assist with daily
activities
• Mechanical ventilation to support breathing
Please visit the myotonic dystrophy section of
our website - www.muscle.ca - for more detailed
information related to:
- Anesthetic Management
- Respiratory Care and Management
- Occupational Therapy
- Physical Therapy
What is the prevalence of myotonic
dystrophy type I?
DM1 is the most common form of adult-onset
muscular dystrophy. On average, occurs in 1 per
8,000 live births, but the prevalence is much higher
in the Saguenay-Saint Laurent area of Quebec
(approximately 1:500).
What about research?
Current efforts in myotonic dystrophy research
are geared to both treatment of the disease and
alleviation of symptoms. A number of molecules
are under investigation for the relief of muscle
spasticity, muscle insulin resistance, and improving
muscle function. Scientists searching for a cure are
investigating means to eliminate toxic RNAs that
accumulate in the cells, or preventing the mutated
gene products from binding and impairing the
function of regulator of alternative splicing, such as
MBNL.
Muscular Dystrophy Canada funds myotonic
dystrophy research. Please visit www.muscle.ca to
learn more about our current research projects.
Where can I get more information?
For up-to-date research information, please visit:
• Muscular Dystrophy Canada: www.muscle.ca
• National Institutes of Health: www.nih.gov
• Orphanet: www.orpha.net
• PubMed: www.pubmed.gov
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Disclaimer:
This document is intended for general information
and awareness. Muscular Dystrophy Canada will
not be held responsible for misuse of information
or any damages incurred as a result of its use.
This resource is not meant to replace consultations
with your doctor or to provide medical advice,
diagnosis, or treatment. For information
specific to the condition affecting you or your
family, please consult your physician.
National Office:
2345 Yonge Street, Suite 900, Toronto, Ontario M4P 2E5
T 416.488.0030 1.866.MUSCLE.8 F 416.488.7523 W muscle.ca
Revised Nov 2013